Portable coordinate measurement machine

ABSTRACT

A portable coordinate measurement machine comprises an articulated arm having jointed arm segments. The arm includes joint assemblies which include at least one read head together with one or more (preferably five) sensors (preferably proximity sensors) in communication with a periodic pattern of a measurable characteristic, the pattern and read heads being positioned within the joint so as to be rotatable with respect to each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of provisional application Nos.60/357,599 filed Feb. 14, 2002 and 60/394,908 filed Jul. 10, 2002, allof the contents of both provisional applications being incorporatedherein by reference and is a continuation-in-part of application Ser.No. 10/366,589 filed Feb. 13, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to coordinate measurement machines(CMMs) and in particular to portable CMMs having an articulated arm.

2. Prior Art

Currently, portable articulated arms are provided as a measurementsystem with a host computer and applications software. The articulatedarm is commonly used to measure points on an object and these measuredpoints are compared to computer-aided design (CAD) data stored on thehost computer to determine if the object is within the CADspecification. In other words, the CAD data is the reference data towhich actual measurements made by the articulated arm are compared. Thehost computer may also contain applications software that guides theoperator through the inspection process. For many situations involvingcomplicated applications, this arrangement is appropriate since the userwill observe the three-dimensional CAD data on the host computer whileresponding to complex commands in the applications software.

An example of a prior art portable CMM for use in the above-discussedmeasurement system is disclosed in U.S. Pat. No. 5,402,582 ('582), whichis assigned to the assignee hereof and incorporated herein by reference.The '582 patent discloses a conventional three-dimensional measuringsystem composed of a manually operated multi-jointed articulated armhaving a support base on one end thereof and a measurement probe at theother end. A host computer communicates to the arm via an intermediatecontroller or serial box. It will be appreciated that in the '582patent, the arm will electronically communicate with the serial boxwhich, in turn, electronically communicates with the host computer.Commonly assigned U.S. Pat. No. 5,611,147 ('147), which is againincorporated herein by reference, discloses a similar CMM having anarticulated arm. In this patent, the articulated arm includes a numberof important features including an additional rotational axis at theprobe end thus providing for an arm with either a two-one-three or atwo-two-three joint configuration (the latter case being a 7 axis arm)as well as improved pre-loaded bearing constructions for the bearings inthe arm.

Still other relevant prior art CMMs include commonly assigned U.S. Pat.No. 5,926,782 ('782), which provides an articulated arm having lockabletransfer housings for eliminating one or more degrees of freedom andU.S. Pat. No. 5,956,857 ('857) which provides an articulated arm havinga quick disconnect mounting system.

More current portable CMMs of the type described herein do notnecessitate the use of an intermediate controller or serial box sincethe functionality thereof is now incorporated in the software providedby the host computer. For example, commonly assigned U.S. Pat. No.5,978,748 ('748), which is incorporated herein by reference, disclosesan articulated arm having an on-board controller which stores one ormore executable programs and which provides the user with instructions(e.g., inspection procedures) and stores the CAD data that serves as thereference data. In the '748 patent, a controller is mounted to the armand runs the executable program which directs the user through a processsuch as an inspection procedure. In such a system, a host computer maybe used to generate the executable program. The controller mounted tothe arm is used to run the executable program but cannot be used tocreate executable programs or modify executable programs. By way ofanalogy to video gaming systems, the host computer serves as theplatform for writing or modifying a video game and the arm mountedcontroller serves as the platform for playing a video game. Thecontroller (e.g., player) cannot modify the executable program. Asdescribed in the '748 patent, this results in a lower cost threedimensional coordinate measurement system by eliminating the need for ahost computer for each articulated arm. U.S. application Ser. No.09/775,236 ('236), assigned to the assignee hereof and incorporatedherein by reference, discloses a method and system for deliveringexecutable programs to users of coordinate measurement systems of thetype disclosed in the '748 patent. The method includes receiving arequest to create an executable program from a customer and obtaininginformation related to the executable program. The executable program isthen developed which guides an operator through a number of measurementsteps to be performed with the three dimensional coordinate measuringsystem. The executable program is delivered to the customer, preferablyover an on-line network such as the Internet.

Commonly assigned U.S. Pat. No. 6,131,299 ('299), (all the contents ofwhich is incorporated herein by reference), discloses an articulated armhaving a display device positioned thereon to allow an operator to haveconvenient display of positional data and system menu prompts. Thedisplay device includes for example, LEDs which indicate system power,transducer position status and error status. U.S. Pat. No. 6,219,928('928), which is assigned to the assignee and incorporated herein byreference, discloses a serial network for the articulated arm. Theserial network communicates data from transducers located in the arm toa controller. Each transducer includes a transducer interface having amemory which stores transducer data. The controller serially addresseseach memory and the data is transferred from the transducer interfacememory to the controller. Commonly assigned U.S. Pat. Nos. 6,253,458('458) and 6,298,569 ('569) both disclose adjustable counter balancemechanisms for articulated arm portable CMMs of the type describedherein.

While well suited for their intended purposes, there is a continued andperceived need in the industry for improved portable CMMs that areeasier to use, more efficient to manufacture, provide improved featuresand can be sold at a lower cost.

SUMMARY OF THE INVENTION

In accordance with the present invention, a portable CMM comprises anarticulated arm having jointed arm segments. In one embodiment, the armsegments include bearing/encoder cartridges which are attached to eachother at predetermined angles using a dual socket joint. Each cartridgecontains at least one, and preferably two, preloaded bearing assembliesand an encoder, preferably an optical encoder, all assembled in acylindrical housing. Preferably, two or more encoder read heads are usedin each joint so as to cause cancellation effects that can be averaged.The arm segments may be threadably interconnected with the arm taperingfrom a wider diameter at its base to a narrower diameter at the probeend.

In accordance with another embodiment of the present invention, one ormore of the jointed arm segments of the articulated arm includesreplaceable protective coverings and/or bumpers to limit high impactshock and abrasion as well as to provide an ergonomically andaesthetically pleasing gripping location.

In still another embodiment of this invention, the articulated armincludes an integrated, internal counter balance in one of the hingejoints. This counter balance utilizes a coil spring having relativelywide end rings and narrower internal rings machined from a metalcylinder. The spring further includes at least two (and preferablythree) posts for locking into the hinge structure of the arm as well asa spring adjustment mechanism.

In still another embodiment of this invention, the articulated armincludes a measurement probe at one end thereof. This measurement probehas an integrally mounted touch trigger probe which is easilyconvertible to a conventional hard probe. The measurement probe alsoincludes improved switches and a measurement indicator light. In oneembodiment, the switches have an arcuate, oblong shape and are easilyarctuatable by the operator. The improved switches include differingcolor, surface texture and/or height which allow the operator to easilydistinguish between them while the indicator light preferably iscolor-coded for ease of operation.

Another embodiment of the present invention includes an articulated armhaving an integral, on-board power supply recharger unit. This powersupply/recharger unit allows for a fully portable CMM and makes it fareasier to use the CMM at a remote location and/or without the need for adirectly cabled articulated arm.

Still another embodiment of the present invention includes anarticulated arm having a measurement probe at one end. The measurementprobe includes a rotatable handle cover and switch assembly whichsurrounds the measurement probe. The rotatable handle cover and switchassembly allows the measurement probe to be more easily held andactivated regardless of hand position. The use of the rotatable handlecover further precludes the necessity for having a third axis ofrotation at the probe end thus allowing for a lower cost and more easilyconstructed portable CMM (relative to 7 axis CMMs or CMMs having a thirdangle of rotation at the measurement probe).

In another embodiment of this invention, a portable CMM includes anarticulated arm having jointed arm segments with a measurement probe atone end thereof and a base at the other end thereof. In accordance witha novel feature of this embodiment, the base has an integrated magneticmount therein for attaching the arm to a magnetic surface. Thisintegrated magnetic mount is preferably threadably connected to thearticulated arm and has an on/off lever for ease of use (which leverpreferably automatically engages when the mount is positioned onto amagnetic surface).

The above-discussed and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are number alike inthe several FIGS.:

FIG. 1 is a front perspective view of the portable CMM of the presentinvention including an articulated arm and attached host computer;

FIG. 2 is a rear perspective view of the CMM of FIG. 1;

FIG. 3 is a right side view of the CMM of FIG. 1 (with the host computerremoved);

FIG. 3A is a right side view of the CMM of FIG. 1 with slightly modifiedprotective sleeves covering two of the long joints;

FIG. 4 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base and the first articulated armsection;

FIG. 5 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base, first arm section and partiallyexploded second arm section;

FIG. 6 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base, first arm section, second armsection and partially exploded third arm section;

FIG. 7 is an exploded, perspective view depicting a pair ofencoder/bearing cartridges being assembled between two dual socketjoints in accordance with the present invention;

FIG. 8 is a front elevation view of the bearing/encoder cartridges anddual socket joints of FIG. 7;

FIG. 9 is an exploded, perspective view of a short bearing/encodercartridge in accordance with the present invention;

FIG. 9A is an exploded, perspective view similar to FIG. 9, but showinga single read head;

FIG. 9B is an exploded, perspective view, similar to FIG. 9, but showingfour read heads;

FIG. 9C is a perspective view of FIG. 9B after assembly;

FIG. 9D is an exploded, perspective view, similar to FIG. 9, but showingthree read heads;

FIG. 9E is a perspective view of FIG. 9D after assembly;

FIG. 10 is a cross-sectional elevation view of the cartridge of FIG. 9;

FIG. 11 is an exploded, perspective view of a long bearing/encodercartridge in accordance with the present invention;

FIG. 11A is an exploded, perspective view similar to FIG. 11, butshowing a single read head;

FIG. 12 is a cross-sectional elevation view of the cartridge of FIG. 11;

FIG. 12A is a cross-sectional elevation view of the cartridge of FIG. 12depicting the dual read heads being rotatable with the shaft;

FIG. 13 is an exploded, perspective view of still anotherbearing/encoder cartridge in accordance with the present invention;

FIG. 13A is an exploded, perspective view similar to FIG. 13, butshowing a single read head;

FIG. 14 is a cross-sectional elevation view of the cartridge of FIG. 13;

FIG. 15 is an exploded, perspective view of a bearing/encoder cartridgeand counter balance spring in accordance with the present invention;

FIG. 15A is an exploded, perspective view similar to FIG. 15, butshowing a single read head;

FIG. 16 is a cross-sectional elevation view of the cartridge and counterbalance of FIG. 15;

FIG. 17 is a top plan view of a dual read head assembly for a largerdiameter bearing/encoder cartridge used in accordance with the presentinvention;

FIG. 18 is a cross-sectional elevation view along the line 18—18 of FIG.17;

FIG. 19 is a bottom plan view of the dual read head assembly of FIG. 17;

FIG. 20 is a top plan view of a dual read head assembly for a smallerdiameter bearing/encoder cartridge in accordance with the presentinvention;

FIG. 21 is a cross-sectional elevation view along the line 21—21 of FIG.20;

FIG. 22 is a bottom plan view of the dual read head assembly of FIG. 20;

FIG. 23A is a block diagram depicting the electronics configuration forthe CMM of the present invention using a single read head and FIG. 23Bis a block diagram depicting the electronics configuration for the CMMof the present invention using a dual read head;

FIG. 24 is a cross-sectional elevation view longitudinally through theCMM of the present invention (with the base removed);

FIG. 24A is a cross-sectional elevation view of the CMM of FIG. 3A;

FIG. 25 is an enlarged cross-sectional view of a portion of FIG. 24depicting the base and first long joint segment of the CMM of FIG. 24;

FIG. 25A is a perspective view of the interconnection between a long andshort joint in accordance with an alternative embodiment of the presentinvention;

FIG. 25B is a cross-sectional elevation view longitudinally through aportion of FIG. 25A;

FIG. 26 is an enlarged cross-sectional view of a portion of FIG. 24depicting the second and third long joint segments;

FIGS. 26A and B are enlarged cross-sectional views of portions of FIG.24A depicting the second and third long joints as well as the probe;

FIG. 27A is an exploded side elevation view depicting the first shortjoint/counter balance assembly in accordance with the present invention;

FIG. 27B is a perspective view depicting the components of FIG. 27A;

FIG. 28 is a cross-sectional elevation view depicting the internalcounter balance of the present invention;

FIG. 29 is a cross-sectional, side elevation view through a firstembodiment of the measurement probe in accordance with the presentinvention;

FIG. 29A is a side elevation view of another embodiment of a measurementprobe in accordance with the present invention;

FIG. 29B is a cross-sectional elevation view along the line 29B—29B ofFIG. 29A;

FIG. 29C is a perspective view of a pair of “take” or “confirm” switchesused in FIGS. 29A-B;

FIGS. 30A-C are sequential elevation plan views depicting the integratedtouch probe assembly and conversion to hard probe assembly in accordancewith the present invention;

FIG. 31 is a cross-sectional, side elevation view through still anotherembodiment of a measurement probe in accordance with the presentinvention;

FIG. 32 is an exploded, perspective view of the integrated magnetic basein accordance with the present invention;

FIG. 33 is a cross-sectional elevation view through the magnetic base ofFIG. 32;

FIG. 34 is a top plan view of the magnetic mount of FIG. 32;

FIG. 35 is a cross-sectional elevation view of a CMM joint from Raab'356 with dual read heads;

FIG. 36 is a cross-sectional elevation view of a CMM joint from Eaton'148 with

dual read heads;

FIG. 37 is a side elevation view of a measurement probe with a seventhaxis transducer;

FIG. 38 is a side elevation view, similar to FIG. 37, but including aremovable handle;

FIG. 39 is an end view of the measurement probe of FIG. 38;

FIG. 40 is a cross-sectional elevation view of the measurement probe ofFIG. 38;

FIG. 41 is a top plan view of a bearing/encoder cartridge employing aread head combined with a plurality of sensors in accordance with thepresent invention;

FIG. 42 is a perspective view of the cartridge of FIG. 41; and

FIG. 43 is an enlarged view of the upper portion of the cartridge ofFIG. 42.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIGS. 1-3, the CMM of the present invention is showngenerally at 10. CMM 10 comprises a multijointed, manually operated,articulated arm 14 attached at one end to a base section 12 and attachedat the other end to a measurement probe 28. Arm 14 is constructed ofbasically two types of joints, namely a long joint (for swivel motion)and a short joint (for hinge motion). The long joints are positionedsubstantially axially or longitudinally along the arm while the shortjoints are preferably positioned at 90° to the longitudinal axis of thearm. The long and short joints are paired up in what is commonly knownas a 2-2-2 configuration (although other joint configurations such as2-1-2, 2-1-3, 2-2-3, etc. may be employed) Each of these joint pairs areshown in FIGS. 4-6.

FIG. 4 depicts an exploded view of the first joint pair, namely longjoint 16 and short joint 18. FIG. 4 also depicts an exploded view of thebase 12 including a portable power supply electronics 20, a portablebattery pack 22, a magnetic mount 24 and a two-piece base housing 26Aand 26B. All of these components will be discussed in more detailhereinafter.

Significantly, it will be appreciated that the diameters of the variousprimary components of articulated arm 14 will taper from the base 12 tothe probe 28. Such taper may be continuous or, as in the embodimentshown in the FIGS., the taper may be discontinuous or step-wise. Inaddition, each of the primary components of articulated arm 14 may bethreadably attached thereby eliminating a large number of fastenersassociated with prior art CMMs. For example, and as will be discussedhereafter, magnetic mount 24 is threadably attached to first long joint16. Preferably, such threading is tapered threading which isself-locking and provides for increased axial/bending stiffness.Alternatively, as shown in FIGS. 25A and 25B, and as discussedhereafter, the primary components of the articulated arm may havecomplimentary tapered male and female ends with associated flanges, suchflanges being bolted together.

Referring to FIG. 5, the second set of a long and short joint is shownbeing attached to the first set. The second joint set includes longjoint 30 and short joint 32. As is consistent with the attachment ofmagnetic mount 24 to long joint 16, long joint 30 is threadably attachedto threading on the interior surface of long joint 16. Similarly, andwith reference to FIG. 6, the third joint set includes a third longjoint 34 and a third short joint 36. Third long joint 34 threadablyattaches to threading on the interior surface of second short joint 32.As will be discussed in more detail hereinafter, probe 28 threadablyattaches to short joint 36.

Preferably, each short joint 18, 32 and 36 is constructed of cast and/ormachined aluminum components or alternatively, lightweight stiff alloyor composite. Each long joint 16, 30 and 34 is preferably constructed ofcast and/or machined aluminum, lightweight stiff alloy and/or fiberreinforced polymer. The mechanical axes of the three aforementionedjoint pairs (i.e., pair 1 comprises joint pairs 16, 18, pair 2 comprisesjoint pairs 30, 32 and pair 3 comprises joint pairs 34, 36) are alignedwith respect to the base for smooth, uniform mechanical behavior. Theaforementioned tapered construction from base 12 to probe 28 ispreferred to promote increased stiffness at the base where loads aregreater and smaller profile at the probe or handle where unobstructeduse is important. As will be discussed in more detail hereinafter, eachshort joint is associated with a protective bumper 38 on either endthereof and each long probe is covered with a protective sleeve 40 or41. It will be appreciated that the first long joint 16 is protected bythe base housing 26A, B which provides the same type of protection assleeves 40, 41 provide for the second and third long joints 30, 34.

In accordance with an important feature of the present invention, eachof the joints of the articulated arm utilizes a modular bearing/encodercartridge such as the short cartridge 42 and the long cartridge 44 shownin FIGS. 7 and 8. These cartridges 42, 44 are mounted in the openings ofdual socket joints 46, 48. Each socket joint 46, 48 includes a firstcylindrical extension 47 having a first recess or socket 120 and asecond cylindrical extension 49 having a second recess or socket 51.Generally, sockets 120 and 51 are positioned 90 degrees to one anotheralthough other relative, angular configurations may be employed. Shortcartridge 42 is positioned in each socket 51 of dual socket joints 46and 48 to define a hinge joint, while long cartridge 44 is positioned insocket 120 of joint 46 (see FIG. 25) and long cartridge 44′ (see FIG.26) is positioned in socket 120 of joint 48 to each define alongitudinal swivel joint. Modular bearing/encoder cartridges 42, 44permit the separate manufacture of a pre-stressed or preloaded dualbearing cartridge on which is mounted the modular encoder components.This bearing encoder cartridge can then be fixedly attached to theexternal skeletal components (i.e., the dual socket joints 46, 48) ofthe articulated arm 14. The use of such cartridges is a significantadvance in the field as it permits high quality, high speed productionof these sophisticated subcomponents of articulated arm 14.

In the embodiment described herein, there are four different cartridgetypes, two long axial cartridges for joints 30 and 34, one base axialcartridge for joint 16, one base cartridge (which includes a counterbalance) for short joint 18 and two hinge cartridges for joints 32 and36. In addition, as is consistent with the taper of articulated arm 14,the cartridges nearest the base (e.g., located in long joint 16 andshort joint 18) have a larger diameter relative to the smaller diametersof joints 30, 32, 34 and 36. Each cartridge includes a pre-loadedbearing arrangement and a transducer which in this embodiment, comprisesa digital encoder. Turning to FIGS. 9 and 10, the cartridge 44positioned in axial long joint 16 will now be described.

Cartridge 44 includes a pair of bearings 50, 52 separated by an innersleeve 54 and outer sleeve 56. It is important that bearings 50, 52 arepre-loaded. In this embodiment, such preload is provided by sleeves 54,56 being of differing lengths (inner sleeve 54 is shorter than outersleeve 56 by approximately 0.0005 inch) so that upon tightening, apreslected preload is generated on bearings 50, 52. Bearings 50, 52 aresealed using seals 58 with this assembly being rotatably mounted onshaft 60. At its upper surface, shaft 60 terminates at a shaft upperhousing 62. An annulus 63 is defined between shaft 60 and shaft upperhousing 62. This entire assembly is positioned within outer cartridgehousing 64 with the shaft and its bearing assembly being securelyattached to housing 64 using a combination of an inner nut 66 and anouter nut 68. Note that upon assembly, the upper portion 65 of outerhousing 64 will be received within annulus 63. It will be appreciatedthat the aforementioned preload is provided to bearings 50, 52 upon thetightening of the inner and outer nuts 66, 68 which provide compressionforces to the bearings and, because of the difference in length betweenthe inner and outer spacers 54, 56, the desired preload will be applied.

Preferably, bearings 50, 52 are duplex ball bearings. In order to obtainthe adequate pre-loading, it is important that the bearing faces be asparallel as possible. The parallelism affects the evenness of thepre-loading about the circumference of the bearing. Uneven loading willgive the bearing a rough uneven running torque feel and will result inunpredictable radial run out and reduced encoder performance. Radial runout of the modularly mounted encoder disk (to be discussed below) willresult in an undesirable fringe pattern shift beneath the reader head.This results in significant encoder angular measurement errors.Furthermore, the stiffness of the preferably duplex bearing structure isdirectly related to the separation of the bearings. The farther apartthe bearings, the stiffer will be the assembly. The spacers 54, 56 areused to enhance the separation of the bearings. Since the cartridgehousing 64 is preferably aluminum, then the spacers 54, 56 will alsopreferably be made from aluminum and precision machined in length andparallelism. As a result, changes in temperature will not result indifferential expansion which would compromise the preload. As mentioned,the preload is established by designing in a known difference in thelength of spacers 54, 56. Once the nuts 66, 68 are fully tightened, thisdifferential in length will result in a bearing preload. The use ofseals 58 provide sealed bearings since any contamination thereof wouldeffect all rotational movement and encoder accuracy, as well as jointfeel.

While cartridge 44 preferably includes a pair of spaced bearings,cartridge 44 could alternatively include a single bearing or three ormore bearings. Thus, each cartridge needs at least one bearing as aminimum.

The joint cartridges of the present invention may either have unlimitedrotation or as an alternative, may have a limited rotation. For alimited rotation, a groove 70 on a flange 72 on the outer surface ofhousing 64 provides a cylindrical track which receives a shuttle 74.Shuttle 74 will ride within track 70 until it abuts a removable shuttlestop such as the rotation stop set screws 76 whereupon rotation will beprecluded. The amount of rotation can vary depending on what is desired.In a preferred embodiment, shuttle rotation would be limited to lessthan 720°. Rotational shuttle stops of the type herein are described inmore detail in commonly owned U.S. Pat. No. 5,611,147, all of thecontents of which have been incorporated herein by reference.

As mentioned, in an alternative embodiment, the joint used in thepresent invention may have unlimited rotation. In this latter case, aknown slip ring assembly is used. Preferably, shaft 60 has a hollow oraxial opening 78 therethrough which has a larger diameter section 80 atone end thereof. Abutting the shoulder defined at the intersectionbetween axial openings 78 and 80 is a cylindrical slip ring assembly 82.Slip ring assembly 82 is non-structural (that is, provides no mechanicalfunction but only provides an electrical and/or signal transferfunction) with respect to the preloaded bearing assembly set forth inthe modular joint cartridge. While slip ring assembly 82 may consist ofany commercially available slip ring, in a preferred embodiment, slipring assembly 82 comprises a H series slip ring available from IDMElectronics Ltd. of Reading, Berkshire, United Kingdom. Such slip ringsare compact in size and with their cylindrical design, are ideallysuited for use in the opening 80 within shaft 60. Axial opening 80through shaft 60 terminates at an aperture 84 which communicates with achannel 86 sized and configured to receive wiring from the slip ringassembly 82. Such wiring is secured in place and protected by a wirecover 88 which snaps onto and is received into channel 86 and aperture84. Such wiring is shown diagrammatically at 90 in FIG. 10.

As mentioned, modular cartridge 44 include both a preloaded bearingstructure which has been described above as well as a modular encoderstructure which will now be described. Still referring to FIGS. 9 and10, the preferred transducer used in the present invention comprises amodular optical encoder having two primary components, a read head 92and a grating disk 94. In this embodiment, a pair of read heads 92 arepositioned on a read head connector board 96. Connector board 96 isattached (via fasteners 98) to a mounting plate 100. Disk 94 ispreferably attached to the lower bearing surface 102 of shaft 60(preferably using a suitable adhesive) and will be spaced from and inalignment with read heads 92 (which is supported and held by plate 100).A wire funnel 104 and sealing cap 106 provide the final outer coveringto the lower end of housing 64. Wire funnel 104 will capture and retainwiring 90 as best shown in FIG. 10. It will be appreciated that theencoder disk 94 will be retained by and rotate with shaft 60 due to theapplication of adhesive at 102. FIGS. 9 and 10 depict a double read head92; however, it will be appreciated that more than two read heads may beused or, in the alternative, a single read head as shown in FIG. 9A maybe used. FIGS. 9B-E depict examples of modular cartridges 44 with morethan two read heads. FIGS. 9B-C show four read heads 92 received in aplate 100 and spaced at 90 degree intervals (although different relativespacings may be appropriate). FIGS. 9D-E show three read heads 92received in a plate 100 and spaced at 120 degree intervals (althoughdifferent relative spacing may be appropriate).

In order to properly align disk 94, a hole (not shown) is providedthrough housing 64 at a location adjacent disk 94. A tool (not shown) isthen used to push disk 94 into proper alignment whereupon adhesivebetween disk 94 and shaft 66 is cured to lock disk 94 in place. A holeplug 73 is then provided through the hole in housing 64.

It is important to note that the locations of disk 94 and read head 92may be reversed whereby disk 94 is attached to housing 56 and read head92 rotates with shaft 60. Such an embodiment is shown in FIG. 12A whereboard 96′ is attached (via adhesive) to shaft 60′ for rotationtherewith. A pair of read heads 92′ are attached to board 96′ and thuswill rotate with shaft 60′. The disk 94′ is positioned on a support 100′which is attached to housing 64′. In any event, it will be appreciatedthat either the disk 94 or read head 92 may be mounted for rotation withthe shaft. All that is important is that disk 94 and read head 92 bepositioned in a cartridge (or joint) so as to be rotatable with respectto each other while maintaining optical communication.

Preferably, the rotational encoder employed in the present invention issimilar to that disclosed in U.S. Pat. Nos. 5,486,923 and 5,559,600, allof the contents of which are incorporated herein by reference. Suchmodular encoders are commercially available from MicroE Systems underthe trade name Pure Precision Optics. These encoders are based onphysical optics that detect the interference between diffraction ordersto produce nearly perfect sinusoidal signals from a photo detector array(e.g., read head(s)) inserted in the fringe pattern. The sinusoidalsignals are electronically interpolated to allow detection ofdisplacement that is only a fraction of the optical fringe.

Using a laser light source, the laser beam is first collimated by a lensand then sized by an aperture. The collimated size beam passes through agrating that diffracts the light into discrete orders with the 0^(th)and all even orders suppressed by the grating construction. With the 0order suppressed, a region exists beyond the diverging 3^(rd) orderwhere only the ±1^(st) orders overlap to create a nearly pure sinusoidalinterference. One or more photodetector arrays (read heads) are placedwithin this region, and produces four channels of nearly pure sinusoidaloutput when there is relative motion between the grating and thedetector. Electronics amplify, normalize and interpolate the output tothe desired level of resolution.

The simplicity of this encoder design yields several advantages overprior art optical encoders. Measurements may be made with only a lasersource and its collimating optics, a diffractive grating, and a detectorarray. This results in an extremely compact encoder system relative tothe bulkier prior art, conventional encoders. In addition, a directrelationship between the grating and the fringe movement desensitizesthe encoder from environmentally induced errors to which prior artdevices are susceptible. Furthermore, because the region of interferenceis large, and because nearly sinusoidal interference is obtainedeverywhere within this region, alignment tolerances are far more relaxedthan is associated with prior art encoders.

A significant advantage of the aforementioned optical encoder is thatthe precision of the standoff orientation and distance or the distanceand orientation of the read head with respect to the encoder disk is farless stringent. This permits a high accuracy rotational measurement andan easy-to-assemble package. The result of using this “geometrytolerant” encoder technology results in a CMM 10 having significant costreductions and ease of manufacturing.

It will be appreciated that while the preferred embodiment describedabove includes an optical disk 94, the preferred embodiment of thepresent invention also encompasses any optical fringe pattern whichallow the read head to measure relative motion. As used herein, suchfringe pattern means any periodic array of optical elements whichprovide for the measurement of motion. Such optical elements or fringepattern could be mounted on a rotating or stationary disk as describedabove, or alternatively, could be deposited, secured or otherwisepositioned or reside upon any of the relatively moving components (suchas the shaft, bearings or housing) of the cartridge.

Indeed, the read head and associated periodic array or pattern does notnecessarily need to be based on optics (as described above) at all.Rather, in a broader sense, the read head could read (or sense) someother periodic pattern of some other measurable quantity orcharacteristic which can be used to measure motion, generally rotarymotion. Such other measurable characteristics may include, for example,reflectivity, opacity, magnetic field, capacitance, inductance orsurface roughness. (Note that a surface roughness pattern could be readusing a read head or sensor in the form of a camera such as a CCDcamera). In such cases, the read head would measure, for example,periodic changes in magnetic field, reflectivity, capacitance,inductance, surface roughness or the like. As used herein therefore, theterm “read head” means any sensor or transducer and associatedelectronics for analysis of these measurable quantities orcharacteristics with an optical read head being just one preferredexample. Of course, the periodic pattern being read by the read head canreside on any surface so long as there is relative (generally rotary)motion between the read head and periodic pattern. Examples of theperiodic pattern include a magnetic, inductive or capacitive mediadeposited on a rotary or stationary component in a pattern. Moreover, ifsurface roughness is the periodic pattern to be read, there is no needto deposit or otherwise provide a separate periodic media since thesurface roughness of any component in communication with the associatedread head (probably a camera such as a CCD camera) may be used.

As mentioned, FIGS. 9 and 10 depict the elements of the modular bearingand encoder cartridge for axially long joint 16. FIGS. 11 and 12 depictthe bearing and encoder cartridge for axial long joints 30 and 34. Thesecartridge assemblies are substantially similar to that shown FIGS. 9 and10 and so are designated by 44′. Minor differences are evident from theFIGS. relative to cartridge 44 with respect to, for example, adifferently configured wire cap/cover 88′, slightly differing wirefunnels/covers 104′, 106′ and the positioning of flange 72′ at the upperend of housing 64′. Also, the flanges between housing 64′ and shaftupper housing 62 are flared outwardly. Of course, the relative lengthsof the various components shown in FIGS. 11 and 12 may differ slightlyfrom that shown in FIGS. 9 and 10. Since all of these components aresubstantially similar, the components have been given the sameidentification numeral with the addition of a prime. FIG. 11A is similarto FIG. 11, but depicts a single read head embodiment.

Turning to FIGS. 13 and 14, similar exploded and cross-sectional viewsare shown for the bearing and encoder cartridges in short hinge joints32 and 36. As in the long axial joints 44′ of FIGS. 11 and 12, thecartridges for the short hinge joints 32 and 36 are substantiallysimilar to the cartridge 44 discussed in detail above and therefore thecomponents of these cartridges are identified at 44″ with similarcomponents being identified using a double prime. It will be appreciatedthat because cartridges 44″ are intended for use in short joints 32, 36,no slip ring assembly is required as the wiring will simply pass throughthe axial openings 78″, 80″ due to the hinged motion of these joints.FIG. 13A is similar to FIG. 13, but depicts a single read headembodiment.

Finally, with reference to FIGS. 15 and 16, the modular bearing/encodercartridge for short hinge joint 18 is shown at 108. It will beappreciated that substantially all of the components of cartridge 108are similar or the same as the components in cartridges 44, 44′ and 44″with the important exception being the inclusion of a counter balanceassembly. This counter balance assembly includes a counter balancespring 110 which is received over housing 64″ and provides an importantcounter balance function to CMM 10 in a manner which will be describedhereinafter with reference to FIGS. 26 to 28. FIG. 15A is similar toFIG. 15, but depicts a single read head embodiment.

As mentioned, in a preferred embodiment, more than one read head may beused in the encoder. It will be appreciated that angle measurement of anencoder is effected by disk run out or radial motion due to appliedloads. It has been determined that two read heads positioned at 180°from each other will result in run out causing cancellation effects ineach read head. These cancellation effects are averaged for a final“immune” angle measurement. Thus, the use of two read heads and theresultant error cancellation will result in a less error prone and moreaccurate encoder measurement. FIGS. 17-19 depict the bottom,cross-sectional and top views respectively for a dual read headembodiment useful in, for example, a larger diameter cartridge such asfound in joints 16 and 18 (that is, those joints nearest the base).Thus, a cartridge end cap 100 has mounted thereto a pair of circuitboards 96 with each circuit board 96 having a read head 92 mechanicallyattached thereto. The read heads 92 are preferably positioned 180° apartfrom each other to provide for the error cancellation resulting from therun out or radial motion of the disk. Each board 96 additionallyincludes a connector 93 for attachment of the circuit board 96 to theinternal bus and/or other wiring as will be discussed hereinafter. FIGS.20-22 depict substantially the same components as in FIGS. 17-19 withthe primary difference being a smaller diameter cartridge end cap 100.This smaller diameter dual read head embodiment would be associated withthe smaller diameter cartridges of, for example, joints 30, 32, 34 and36.

The use of at least two read heads (or more such as the three readsheads shown in FIGS. 9D-E and the four read heads shown in FIGS. 9B-C)is also advantageously employed in more conventional coordinatemeasurement machines to significantly reduce the cost and complexity ofmanufacture thereof. For example, a coordinate measurement machinedescribed in U.S. Pat. No. 5,794,356 (hereinafter “Raab '356”),incorporated herein by reference, includes a relatively simpleconstruction for each joint including a first housing that remainsstationary with one joint half, and a second housing that remainsstationary with the second joint half, the first and second housingshaving pre-loaded bearings that allow them to rotate with each other.The first housing retains a packaged encoder and the second housingincludes an axially-disposed internal shaft that extends into the firsthousing and mates with the encoder shaft protruding from the packagedencoder. The prior art packaged encoder required that there be no loadsapplied thereto and that the motion of the second housing be accuratelytransmitted to the encoder despite small misalignments of the axis ofthe internal shaft and the axis of the packaged encoder to maintain thehighly accurate rotational measurements. To accommodate manufacturingtolerances in axial misalignment, a special coupling device is connectedbetween the encoder shaft and the internal shaft. Such a structure canbe seen in FIG. 7 of Raab '356.

In contrast, FIG. 35 shows a modified structure 400 in which thecoupling device and packaged encoder from the Raab '356 CMM are removedand replaced with encoder disk 96 and end cap 100. Here, two joints arepositioned at 90° to each other, each joint having a first housing 420and a second housing 410. Internal shaft 412 extends from second housing420 into first housing 410. As shown, encoder disk 96 is attached, e.g.,using adhesive, to the end of internal shaft 412 while end cap 100 isfixed within first housing 420. However, it will be understood thatencoder disk 96 may be fixed within first housing 420 and end cap 100 befixed to internal shaft 412 without affecting the operation of thejoint.

As previously described, the use of two (or more) read heads and theresultant error cancellation will result in a less error prone and moreaccurate encoder measurement despite small axial misalignments. Inaddition, a direct relationship between the grating and the fringemovement desensitizes the encoder from environmentally induced errors towhich prior art devices are susceptible. Furthermore, because the regionof interference is large, and because nearly sinusoidal interference isobtained everywhere within this region, alignment tolerances are farmore relaxed than is associated with prior art encoders as previouslydescribed.

In another example, U.S. Pat. No. 5,829,148 to Eaton (hereinafter “Eaton'148”), incorporated herein by reference, describes a prior art CMM inwhich a packaged encoder forms an integral part of each joint byproviding primary rotational bearings, therefore avoiding any need tocompensate for axial misalignments as required in Raab '356 discussedabove. However, because the encoder provides primary rotationalbearings, it is important that the encoder be structurally rugged andable to be subjected to various loadings without affecting itsperformance. This adds to the cost and bulkiness of the encoder. Such astructure can be seen in FIG. 4 of Eaton '148.

In contrast, FIG. 36 shows a modified structure 450 in which thepackaged encoder and connecting shaft of one joint from the Eaton '148CMM is removed and replaced by end cap 100 and encoder disk 96. Here afirst housing 470 retains end cap 100 and retains internal shaft 462 ofsecond housing 460 by bearings 472. Internal shaft 462 is extended toterminate proximate end cap 100 and encoder disk 96 is attached, e.g.,using adhesive, at the end of internal shaft 462. As in the embodimentshown in FIG. 35, the use of two (or more) read heads significantlyreduces the cost and complexity of the joint without sacrificingaccuracy.

It will be appreciated that non-circularity of the motion of theperiodic pattern is the primary cause for inaccuracies in a rotationaltransducer of the types described herein. This non-circularity of motioncan be due to a number of phenomena including assembly imperfections andexternal deformations. External deformations can occur anywhere in theCMM and most generally occur with respect to the bearing structureand/or the joint tubing. For example, such external deformation canresult from non-repeatable bearing run-out, bearing wobble, bearingdeformation, thermal affects and bearing play. As discussed with respectto FIGS. 17-21, in one embodiment of this invention, the inaccuracies ofthe rotational transducers are corrected for using at least two readheads, preferably mounted at 180° apart from each other. However, instill another embodiment of this invention shown in FIGS. 41-43, thepossible error derived from deformations to the CMM and/or assemblyimperfections are corrected using a combination of at least one readhead with one or more sensors, preferably a plurality of proximitysensors (or any other sensor which measures displacement).

It will be appreciated that in any given cartridge of the type describedherein, there are six degrees of freedom between the shaft and thehousing of the cartridge. That is, the shaft includes six degrees offreedom, namely X, Y and Z axis displacement and X, Y, and Z axisrotation. Turning now to FIGS. 41-43, a cartridge of the type describedabove is shown at 600. Cartridge 600 includes an internal shaft 602rotationally mounted on bearings (not shown) within a housing 606. Readhead plate 604 secures an encoder read head 610 and sensors S1-S5 tohousing 606. An encoder disk 608 having an optical fringe patternthereon is attached to shaft 602 for rotation therewith. Encoder readhead 610 (attached to read head plate 604) is mounted above opticalfringe pattern 608 and preferably functions to measure Z axis rotationof shaft 602. In addition to read head 610, cartridge 600 includes fiveadditional sensors, all of which are fixed to housing 606 through readhead plate 604; and all of which are intended to measure relativemovement between the shaft 602 and housing 606. These additional sensorsinclude a displacement sensor S1 for measuring Y axis displacement ofshaft 602 (with respect to housing 606) and a displacement sensor S2 formeasuring X axis displacement of shaft 602 (with respect to housing606). Thus, shaft 602 has associated with it three sensors, namely readhead 610 and sensors S1 and S2 for respectively measuring the Z axisrotation and the X and Y axis displacement thereof. Preferably, theshaft 602 includes three additional sensors associated with it formeasuring X and Y axis rotation and Z axis displacement. Specifically,sensors S3, S4 and S5 in combination measure the X and Y axis ofrotation as well as the Z axis displacement. In the embodiment shown inFIGS. 41-43, the S3, S4 and S5 sensors are spaced along the read headplate 604 at 120° intervals. The measurements from these equidistantlyspaced three sensors are combined in a known manner to determine thecombined X and Y axis rotation and Z axis displacement.

Thus, these additional five sensors S1-S5 measure and correct for anydeformations in the CMM including the joint tubes or the bearingstructure and these sensors can be used to correct for such error inmeasurement. These additional sensors are therefore used to measurerelative motions between the shaft and housing to determine movementsother than the rotary movement of the disk and therefore correct for anyerrors caused by these “other” movements. Any suitable type of sensorfor carrying out these displacement measurements may be used inaccordance with the present invention. Preferably the sensors areproximity sensors such as proximity sensors using Hall effects, orproximity sensors based on magneto, resistive, capacitive or opticalcharacteristics.

It will be appreciated that, when for example, a joint is placed underload and the bearing structure deforms (and as a result of suchdeformation, the shaft 602 carrying the optical pattern 608 and thehousing 606 with the read head 610 will move with respect to eachother), the angular measurement which will be affected by such movementwill be “corrected” using the displacement information from theadditional sensors S1-S5 (it being appreciated that the presentinvention contemplates the use of all or less than all of the sensorsS1-S5 and moreover further contemplates the use of sensors in additionto S1 through S5). This correction results in substantially improvedaccuracy for the portable CMM. It will further be appreciated that whilethe invention contemplates at least one of the joint cartridgesincluding additional sensors S1-S5, in a preferred embodiment, all ofthe cartridges would include such additional sensors. Also, while theFIGS. 41-43 embodiment is shown with a rotary encoder having an opticalgrating disk, any of the alternative rotary encoders describedpreviously which detect and analyze a periodic pattern of a measurablecharacteristic including those employing measurable characteristics sucha reflectivity, opacity, magnetic field, capacitance, inductance orsurface roughness, may be utilized with the sensors S1-S5 as describedherein. Also, while the FIGS. 41-43 embodiment depict an embodimentwherein the optical disk rotates with the shaft 602, the multiplesensors S1-S5 may also be used with an embodiment such as that shown inFIG. 12A where the optical disk is stationary.

While, as discussed above, the additional sensors could be used tocorrect for errors caused by bearing and other arm deformations, theadditional sensors may also be used to calculate and measure theexternal forces directed at the joint which are actually causing suchstructural deformation. These measurements may be advantageouslyutilized so as to provide sensory feedback to the user. For example,certain ranges of external forces can be tolerated on a particularbearing structure or joint; however, the sensing of external forces bydeformation of the bearing arrangement can be used to indicate thatthese ranges have been exceeded and thereafter provide sensory feedbackto the user so as to take remedial action to alleviate such externalforces. That is, the user can then modify the handling of the CMM inorder to improve the measurement. This sensory feedback may be in theform of auditory and/or visual feedback; and may be indicated bysoftware controlling the CMM. Thus, the additional sensors S1-S5described above can act as overload sensors and prevent the user fromoverstressing the arm and thereby maintain optimum precision so as toinsure precise measurement. Indeed, the measurement of the externalforce on a given joint may be utilized not only with the embodiment ofFIGS. 41-43 (wherein additional sensors S1-S5 are employed) but alsowith the above-discussed embodiments wherein two or more read heads areemployed. In the case of the two read head arrangement, the angularmeasurement is derived from the average of the two read heads. The forceof deformation can then be obtained by measuring the difference betweenthe two read head readings. In the case of the FIGS. 41-43 embodiments,the deformation can be measured in the direction of each of the twoproximity sensors. This provides additional directional information.Using all six sensors (S1-S5 and the read head) will provide a totaldescription of the deformations in each of the joints due to themeasurement of all six degrees of freedom.

In addition to the improvements in the angular accuracy of thetransducer provided by either the use of two read heads or the use of asingle read head together with one or more proximity sensors, theinformation derived from measuring the force of deformation can also beused to correct the kinematics of the arm by using such deformationinformation to change the dimension of the arm in real time and therebyimprove the accuracy of the measurement. Thus, for example, if thebearings are deformed, this deformation will cause a change in thelength of a segment of the arm. By measuring this deformation using thesensors and read heads as described herein, this change in the length ofthe arm can be taken into account in the measurement software associatedwith the CMM and then used as a correction to improve the ultimatemeasurement accuracy of the arm.

Turning now to FIG. 23A, a block diagram of the electronics is shown forthe single read head embodiment of FIGS. 9A, 11A, 13A and 15A. It willbe appreciated that CMM 10 preferably includes an external bus(preferably a USB bus) 260 and an internal bus (preferably RS-485) 261which is designed to be expandable for more encoders as well as eitheran externally mounted rail or additional rotational axes such as aseventh axis. The internal bus is preferably consistent with RS485 andthis bus is preferably configured to be used as a serial network in amanner consistent with the serial network for communicating data fromtransducers in a portable CMM arm as disclosed in commonly assigned U.S.Pat. No. 6,219,928, all of the contents of which have been incorporatedherein by reference.

With reference to FIG. 23A, it will be appreciated that each encoder ineach cartridge is associated with an encoder board. The encoder boardfor the cartridge in joint 16 is positioned within base 12 and isidentified at 112 in FIG. 25. The encoders for joints 18 and 30 areprocessed on a dual encoder board which is located in the second longjoint 30 and is identified at 114 in FIG. 26. FIG. 26 also depicts asimilar dual encoder board 116 for the encoders used in joints 32 and34, board 116 being positioned in third long joint 34 as shown in FIG.26. Finally, the end encoder board 118 is positioned within measurementprobe handle 28 as shown in FIG. 24 and is used to process the encodersin short joint 36. Each of the boards 114, 116 and 118 are associatedwith a thermocouple to provide for thermal compensation due totemperature transients. Each board 112, 114, 116 and 118 incorporatesembedded analog-to-digital conversion, encoder counting and serial portcommunications. Each board also has read programmable flash memory toallow local storage of operating data. The main processor board 112 isalso field programmable through the external USB bus 260. As mentioned,the internal bus (RS-485) 261 is designed to be expandable for moreencoders which also includes either an externally mounted rail and/orseventh rotation axis. An axis port has been provided to provideinternal bus diagnosis. Multiple CMMs of the type depicted at 10 inthese FIGURES may be attached to a single application due to thecapabilities of the external USB communications protocol. Moreover,multiple applications may be attached to a single CMM 10 for the verysame reasons.

Preferably, each board 112, 114, 116 and 118 includes a 16-bit digitalsignal processor such as the processor available from Motorola under thedesignation DSP56F807. This single processing component combines manyprocessing features including serial communication, quadrature decoding,A/D converters and on-board memory thus allowing a reduction of thetotal number of chips needed for each board.

In accordance with another important feature of the present invention,each of the encoders is associated with an individualized identificationchip 121. This chip will identify each individual encoder and thereforewill identify each individual bearing/encoder modular cartridge so as toease and expedite quality control, testing, and repair.

FIG. 23B is an electronics block diagram which is similar to FIG. 23A,but depicts the dual read head embodiment of FIGS. 10, 12, 14 and 16-22.

With reference to FIGS. 24-26, the assembly of each cartridge in thearticulated arm 14 will now be described (note that FIG. 24 depicts arm10 without base 12. Note also that FIGS. 24-26 employ the single readhead embodiments of FIGS. 9A, 11A, 13A and 15A). As shown in FIG. 25,the first long joint 16 includes a relatively long cartridge 44, theupper end of which has been inserted into a cylindrical socket 120 ofdual socket joint 46. Cartridge 44 is securely retained within socket120 using a suitable adhesive. The opposite, lower end of cartridge 44is inserted into an extension tube, which in this embodiment may be analuminum sleeve 122 (but sleeve 122 may also be comprised of a stiffalloy or composite material). Cartridge 44 is secured in sleeve 122again using a suitable adhesive. The lower end of sleeve 122 includes alarger outer diameter section 124 having internal threading 126 thereon.Such threading is outwardly tapered and is configured to threadably matewith inwardly tapered threading 128 on magnetic mount housing 130 as isclearly shown in FIG. 4. As has been discussed, all of the severaljoints of CMM 10 are interconnected using such tapered threading.Preferably, the tapered thread is of the NPT type which isself-tightening and therefore no lock nuts or other fastening devicesare needed. This threading also allows for and should include a threadlocking agent.

Turning to FIG. 26, as in first long joint 16, long cartridge 44′ isadhesively secured in the cylindrical opening 120′ of dual socket joint46′. The outer housing 64′ of cartridge 44′ includes a shoulder 132defined by the lower surface of flange 72′. This shoulder 132 supportscylindrical extension tube 134 which is provided over and surrounds theouter surface of housing 64′. Extension tubes are used in the joints tocreate a variable length tube for attachment to a threaded component.Extension tube 134 thus extends outwardly from the bottom of cartridge64′ and has inserted therein a threaded sleeve 136. Appropriate adhesiveis used to bond housing 44′ to extension tube 134 as well as to bondsleeve 136 and tube 134 together. Sleeve 136 terminates at a taperedsection having outer threading 138 thereon. Outer threading threadablymates with internal threading 140 on connecting piece 142 which has beenadhesively secured in opening 144 of dual socket joint 48. Preferably,extension tube 134 is composed of a composite material such as anappropriate carbon fiber composite while threadable sleeve 136 iscomposed of aluminum so as to match the thermal properties of the dualsocket joint 48. It will be appreciated that PC board 114 is fastened toa support 146 which in turn is secured to dual socket joint support 142.

In addition to the aforementioned threaded connections, one, some or allof the joints may be interconnected using threaded fasteners as shown inFIGS. 25A-B. Rather than the threaded sleeve 136 of FIG. 26, sleeve 136′of FIG. 25B has a smooth tapered end 137 which is received in acomplimentary tapered socket support 142′. A flange 139 extendscircumferentially outwardly from sleeve 136′ with an array of bolt holes(in this case 6) therethrough for receiving threaded bolts 141. Bolts141 are threadably received in corresponding holes along the uppersurface of socket support 142′. An extension tube 134′ is received oversleeve 136′ as in the FIG. 26 embodiment. The complimentary tapered maleand female interconnections for the joints provide improved connectioninterfaces relative to the prior art.

Still referring to FIG. 26, long cartridge 44″ of third long joint 34 issecured to arm 14 in a manner similar to cartridge 44′ of long joint 30.That is, the upper portion of cartridge 44″ is adhesively secured intoan opening 120″ of dual socket joint 46″. An extension tube 148(preferably composed of a composite material as described with respectto tube 134) is positioned over outer housing 64″ and extends outwardlythereof so as to receive a mating sleeve 150 which is adhesively securedto the interior diameter of extension tube 148. Mating sleeve 150terminates at a tapered section having outer threading 152 and mateswith complimentary interior threading 153 on dual socket joint support154 which has been adhesively attached to a cylindrical socket 156within dual socket joint 148′. Printed circuit board 116 is similarlyconnected to the dual socket joint using the PCB support 146′ which issecured to dual socket joint support 154.

As discussed with respect to FIGS. 7 and 8, the short cartridges 44′ inFIGS. 13 and 14 and 108 of FIG. 15 are simply positioned between twodual socket joints 46, 48 and are secured within the dual socket jointsusing an appropriate adhesive. As a result, the long and shortcartridges are easily attached to each other at right angles (or, ifdesired, at angles other than right angles).

The modular bearing/transducer cartridges as described above constitutean important technological advance in portable CMMs such as shown, forexample, in the aforementioned Raab '356 and Eaton '148 patents. This isbecause the cartridge (or housing of the cartridge) actually defines astructural element of each joint which makes up the articulated arm. Asused herein, “structural element” means that the surface of thecartridge (e.g., the cartridge housing) is rigidly attached to the otherstructural components of the articulated arm in order to transferrotation without deformation of the arm (or at most, with only deminimis deformation). This is in contrast to conventional portable CMMs(such as disclosed in the Raab '356 and Eaton '148 patents) whereinseparate and distinct joint elements and transfer elements are requiredwith the rotary encoders being part of the joint elements (but not thetransfer elements). In essence, the present invention has eliminated theneed for separate transfer elements (e.g., transfer members) bycombining the functionality of the joint and transfer elements into asingular modular component (i.e., cartridge). Hence, rather than anarticulated arm comprised of separate and distinct joints and transfermembers, the present invention utilizes an articulated arm made up of acombination of longer and shorter joint elements (i.e., cartridges), allof which are structural elements of the arm. This leads to betterefficiencies relative to the prior art. For example, the number ofbearings used in a joint/transfer member combination in the '148 and'582 patent was four (two bearings in the joint and two bearings in thetransfer member) whereas the modular bearing/transducer cartridge of thepresent invention may utilize a minimum of one bearing (although twobearings are preferred) and still accomplish the same functionality(although in a different and improved way).

FIGS. 24A and 26A-B are cross-sectional views, similar to FIGS. 24-26,but showing the dual read head embodiments of FIGS. 10, 12, 14 and 16-22and are further cross-sections of the CMM 10′ shown in FIG. 3A.

The overall length of articulated arm 14 and/or the various arm segmentsmay vary depending on its intended application. In one embodiment, thearticulated arm may have an overall length of about 24 inches andprovide measurements on the order of about 0.0002 inch to 0.0005 inch.This arm dimension and measurement accuracy provides a portable CMMwhich is well suited for measurements now accomplished using typicalhand tools such as micrometers, height gages, calipers and the like. Ofcourse, articulated arm 14 could have smaller or larger dimensions andaccuracy levels. For example, larger arms may have an overall length of8 or 12 feet and associated measurement accuracies of 0.001 inch thusallowing for use in most real time inspection applications or for use inreverse engineering.

CMM 10 may also be used with a controller mounted thereto and used torun a relatively simplified executable program as disclosed inaforementioned U.S. Pat. No. 5,978,748 and application Ser. No.09/775,226; or may be used with more complex programs on host computer172.

With reference to FIGS. 1-6 and 24-26, in a preferred embodiment, eachof the long and short joints are protected by an elastomeric bumper orcover which acts to limit high impact shock and provide ergonomicallypleasant gripping locations (as well as an aesthetically pleasingappearance). The long joints 16, 30 and 34 are all protected by a rigidplastic (e.g., ABS) replaceable cover which serves as an impact andabrasion protector. For the first long joint 16, this rigid plasticreplaceable cover comes in the form of the two-piece base housing 26Aand 26B as is also shown in FIG. 4. Long joints 30 and 34 are eachprotected by a pair of cover pieces 40 and 41 which, as shown in FIGS. 5and 6 may be fastened together in a clam shell fashion using appropriatescrews so as to form a protective sleeve. It will be appreciated that ina preferred embodiment, this rigid plastic replaceable cover for eachlong joint 30 and 34 will surround the preferably composite (carbonfiber) extension tube 134 and 148, respectively.

Preferably, one of the covers, in this case cover section 41, includes aslanted support post 166 integrally molded therein which limits therotation at the elbow of the arm so as to restrict probe 28 fromcolliding with base 12 in the rest position. This is best shown in FIGS.3, 24 and 26. It will be appreciated that post 166 will thus limitunnecessary impact and abrasion.

As will be discussed with respect to FIGS. 29 and 31, probe 28 may alsoinclude a replaceable plastic protective cover made from a rigid plasticmaterial.

FIGS. 3A, 24A and 26A-B depict alternative protective sleeves 40′, 41′which also have a clam shell construction, but are held in place usingstraps or spring clips 167 rather than threaded fasteners.

Each of the short joints 18, 32 and 36 include a pair of elastomeric(e.g., thermoplastic rubber such as Santoprene®) bumpers 38 aspreviously mentioned and as shown clearly in FIGS. 1-3 and 5-6. Bumpers38 may either be attached using a threaded fastener, a suitable adhesiveor in any other suitable manner. Elastomeric or rubber bumper 38 willlimit the high impact shock as well as provide an aesthetically pleasingand ergonomically pleasant gripping location.

The foregoing covers 40, 41, 40′, 41′ and bumpers 38 are all easilyreplaceable (as is the base housing 26A, 26B) and allow arm 14 toquickly and inexpensively be refurbished without influencing themechanical performance of CMM 10.

Still referring to FIGS. 1-3, base-housing 26A, B includes at least twocylindrical bosses for the mounting of a sphere as shown at 168 in FIG.3. The sphere may be used for the mounting of a clamp type computerholder 170 which in turn supports a portable or other computer device172 (e.g., the “host computer”). Preferably, a cylindrical boss isprovided on either side of base housing 26A, B so that the ball andclamp computer mount may be mounted on either side of CMM 10.

Turning now to FIGS. 15, 16, 27A, B and 28, the preferred counterbalance for use with CMM 10 will now be described. Conventionally,portable CMMs of the type described herein have utilized an externallymounted coil spring which has been mounted separately in outriggerfashion on the outside of the articulated arm for use as a counterbalance. In contrast, the present invention utilizes a fully integratedinternal counter balance which leads to a lower overall profile for thearticulated arm. Typically, prior art counter balances have utilizedwound coil springs in the counter balance mechanism. However, inaccordance with an important feature of the present invention, thecounter balance employs a machined coil spring (as opposed to a woundcoil spring). This machined spring 110 is shown in FIGS. 16 and 27A-Band is formed from a single cylinder of metal (steel) which is machinedto provide a pair of relatively wide rings 174, 176 at opposed ends ofthe coil and relatively narrower rings 178 forming the intermediatecoils between end coils 174, 176. It will be appreciated that the widerend rings 174, 176 engage with the respective side surfaces 180 of shaft62′ and 182 of housing 64″ thereby preventing lateral movement of spring110. The wider, solid end rings 174, 176 act as an anti-twist device andprovide superior function relative to prior art wound springs. End ring174 preferably includes a pair of locking posts 184, 186 (although onlyone locking post may be employed) while end ring 176 includes a lockingpost 188.

With reference to FIG. 27B, each dual socket joint 46, 48 includeschannels such as shown at 190 and 191 in dual socket joint 46 forreceiving a respective post 184, 186 or 188. With reference to FIG. 28,while pins 184, 186 will remain in a fixed position within theappropriate channel or groove of dual socket joint 48, the location ofpin 188 may be changed so as to optimize the overall wind-up on spring110 and provide the most efficient counter balance force. This isaccomplished using a threaded hole 192 which receives threaded screw194. As shown in FIG. 28, screw 194 may be operated on to contact pin188 and move pin 188 circumferentially in a clock-wise direction alonginterior channel 696 which is shown in FIG. 27B as being perpendicularto pin access groove 190. Screw 194 is preferably positioned to optimizespring 110 in the factory.

It will be appreciated that during use of articulated arm 14, theencoder/bearing cartridge 108 will act as a hinge joint and onceinserted and adhesively secured within the sockets of dual socket joints46, 48, pins 184, 186 and 188 will be locked in their respectivegrooves. When socket joint 48 is rotated relative to socket joint 46(via the hinge joint of cartridge 108), spring 110 will wind-up. When itis desired that socket joint 48 rotate back to its original position,the wound forces of spring 110 will unwind providing the desired counterbalance force.

In the event that it is desired that articulated arm 14 be mountedupside down such as on a grinder, beam or ceiling, the orientation ofspring 110 may similarly be inverted (or reversed) so that the properorientation for the necessary counterbalance may be achieved.

Turning now to FIGS. 29 and 30A-C, a preferred embodiment of themeasurement probe 28 will now be described. Probe 28 includes a housing196 having an interior space 198 therein for housing printed circuitboard 118. It will be appreciated that housing 196 constitutes a dualsocket joint of the type described above and includes a socket 197 inwhich is bonded a support member 199 for supporting circuit board 118.Preferably, handle 28 includes two switches, namely a take switch 200and a confirm switch 202. These switches are used by the operator toboth take a measurement (take switch 200) and to confirm the measurement(confirm switch 202) during operation. In accordance with an importantfeature of this invention, the switches are differentiated from eachother so as to minimize confusion during use. This differentiation maycome in one or more forms including, for example, the switches 200, 202being of differing height and/or differing textures (note that switch202 has an indentation as opposed to the smooth upper surface of switch200) and/or different colors (for example, switch 200 may be green andswitch 202 may be red). Also in accordance with an important feature ofthis invention, an indicator light 204 is associated with switches 200,202 for indicating proper probing. Preferably, the indicator light 204is a two-color light so that, for example, light 204 is green upontaking of a measurement (and pressing the green take button 200) and isred for confirming a measurement (and pressing the red button 202). Theuse of a multicolored light is easily accomplished using a known LED asthe light source for light 204. To assist in gripping, to provideimproved aesthetics and for impact resistance, an outer protectingcovering of the type described above is identified at 206 and providedover a portion of probe 28. A switch circuit board 208 is provided forthe mounting of buttons 200, 202 and lamp 204 and is supported bysupport member 199. Switch board 208 is electrically interconnected withboard 118 which houses components for processing the switches and lightindicator as well as for the processing of short hinge joint 36.

In accordance with another important feature of the present invention,and with reference to both FIG. 29 as well as FIGS. 30A-C, probe 28includes a permanently installed touch trigger probe as well as aremovable cap for adapting a fixed probe while protecting the touchtrigger probe. The touch probe mechanism is shown at 210 in FIG. 29 andis based on a simplified three point kinematics seat. This conventionalconstruction comprises a nose 212 which contacts a ball 214 biased by acontact spring 216. Three contact pins (one pin being shown at 218) arein contact with an underlying electric circuit. Application of anyforces against the probe nose 212 results in lifting of any one of thethree contact pins 218 resulting in an opening of the underlyingelectric circuit and hence activation of a switch. Preferably, touchtrigger probe 210 will operate in conjunction with the front “take”switch 200.

As shown in FIG. 30B, when using touch trigger probe 210, a protectivethreaded cover 220 is threadably attached to threading 222 surroundingtrigger probe 210. However, when it is desired to use a fixed proberather than the touch trigger probe, the removable cap 220 is removedand a desired fixed probe such as that shown at 224 in FIGS. 29 and30A-C is threadably attached to threading 222. It will be appreciatedthat while fixed probe 224 has a round ball 226 attached thereto, anydifferent and desired fixed probe configuration may be easily threadablyattached to probe 28 via threading 222. Touch trigger probe assembly 210is mounted in a housing 228 which is threadably received into threadedconnector 230 which forms a part of probe housing 196. This threadableinterconnection provides for the full integration of touch trigger probe210 into probe 28. The provision of a fully integrated touch proberepresents an important feature of the present invention and isdistinguishable from prior art detachable touch probes associated withprior art CMMs. In addition, the permanently installed touch triggerprobe is also easily convertible to a hard probe as described above.

FIGS. 29A-C disclose yet another preferred embodiment for a measurementprobe in accordance with the present invention. In FIGS. 29A-C, ameasurement probe is shown at 28′ and is substantially similar tomeasurement probe 28 in FIG. 29 with the primary difference residing inthe configuration of the “take” and “confirm” switches. Rather than thediscrete button type switches shown in FIG. 29, measurement probe 28′utilizes two pairs of arcuate oblong switches 200 a-b and 202 a-b. Eachrespective pair of oblong switches 202 a-b and 200 a-b correspondrespectively to the take switch and the confirm switch as describedabove with respect to FIG. 29. An advantage of the measurement probe 28′embodiment relative to the measurement probe 28 embodiment is that eachpair of oblong switches 202 and 200 surround virtually the entirecircumference (or at least the majority of the circumference) of themeasurement probe and therefore are more easily actuatable by theoperator of the portable CMM. As in the FIG. 29 embodiment, an indicatorlight 204 is associated with each switch with the light 204 and switches200, 202 being mounted on respective circuit boards 208′. Also, as inthe FIG. 29 embodiment, switches 200, 202 may be differentiated usingfor example, different heights, different textures and/or differentcolors. Preferably, switches 200, 202 have a slight float such that thebutton may be actuated when pressed down in any location therealong. Asin the FIG. 29 embodiment, an outer protective covering of the typedescribed above is used at 206 and provided over a portion of probe 28′.

Referring now to FIG. 31, an alternative measurement probe for use withCMM 10 is shown generally at 232. Measurement probe 232 is similar tomeasurement probe 28 of FIG. 29 with the primary difference being thatprobe 232 includes a rotating handle cover 234. Rotating cover 234 ismounted on a pair of spaced bearings 236, 238 which in turn are mountedon an inner core or support 240 such that cover 234 is freely rotatable(via bearings 236, 238) about inner core 240. Bearings 236, 238 arepreferably radial bearings and minimize the parasitic torques on the armdue to probe handling. Significantly, the switch plate 208′ andcorresponding switches 200′, 202′ and LED 204′ are all mounted torotating handle cover 234 for rotation therewith. During rotation,electrical connectivity to processing circuit board 118′ is providedusing a conventional slip ring mechanism 242 which comprises a knownplurality of spaced spring fingers 242 which contact stationary circularchannels 244. In turn, these contact channels 244 are electricallyconnected to circuit board 118′. The rotating handle cover 234 andswitch assembly is thus electrically coupled to the inner core or probeshaft 240 and electronics board 118′ using the slip ring conductor 242.The rotation of the probe handle 234 permits switches 200′, 202′ to beoriented conveniently for the user. This allows the articulated arm 14′to measure accurately during handling by minimizing undocumented forces.The cover 234 is preferably comprised of a rigid polymer and is providedwith appropriate indentations 246 and 248 to allow easy and convenientgripping and manipulation by the probe operator.

It will be appreciated that the remainder of probe 232 is quite similarto probe 28 including the provision of a permanently and integrallyinstalled touch probe 210 in cover 220. Note that switches 200′, 202′are of differing heights and surface textures so as to provide ease ofidentification.

The rotating cover 234 is a significant advance in the CMM field in thatit can alleviate the need for a seventh axis of rotation at the probesuch as disclosed in aforementioned U.S. Pat. No. 5,611,147. It will beappreciated that the addition of a seventh axis leads to a more complexand expensive CMM as well as the addition of possible error into thesystem. The use of the rotatable probe 232 alleviates the need for a“true” seventh axis as it permits the probe to provide the rotationneeded for handle position at the probe end without the complexity of aseventh transducer and associated bearings, encoder and electronics.

In the event that it is desired to utilize a measurement probe having a“true” seventh axis, that is, having a measurement probe with a seventhrotary encoder for measuring rotary rotation, such a measurement probeis shown in FIGS. 37-40. With reference to such FIGS., a measurementprobe 500 is shown with such measurement probe being substantiallysimilar to the measurement probe in FIG. 29 with the primary differencebeing the insertion of a modular bearing/transducer cartridge 502 of thetype described above, the presence of the take and confirm switches 504,506 on the sides of the measurement probe and the inclusion of aremovable handle 508.

It will be appreciated that the modular bearing/transducer cartridge 502is substantially similar to the cartridges described in detail above andinclude a rotatable shaft, a pair of bearings on the shaft, an opticalencoder disk, at least one and preferably two optical read heads spacedfrom and in optical communication with the encoder disk and a housingsurrounding the bearings, optical encoder disk, read head(s) and atleast a portion of the shaft so as to define the discrete modularbearing/transducer cartridge. A circuit board 503 for the encoderelectronics resides in an opening 505 with probe 500. Pairs of take andconfirm buttons 504, 506 are positioned on either side of a downwardlyprojected housing portion 510 of probe 500 with the buttons beingconnected to an appropriate PC board 512 as in the measurement probe ofthe FIG. 29 embodiment. Similarly, an indicator light 513 is positionedbetween buttons 504, 506 as in the previously discussed embodiments. Apair of threaded openings 514 in housing 510 receive fasteners forremovable attachment of handle 508 which provides for ease of rotarymanipulation during use of measurement probe 500.

In all other substantial respects, measurement probe 500 is similar tomeasurement probe 28 of FIG. 29 including the preferred use ofpermanently installed touch trigger probe at 516 as well as a removablecap for adapting a fixed probe 518 while protecting the touch triggerprobe. It will be appreciated that the seventh rotary encoder 502included in measurement probe 500 facilitates the use of CMM 10 inconnection with known laser line scanners and other peripheral devices.

Turning now to FIGS. 2-4, 23 and 25, in accordance with an importantfeature of the present invention, a portable power supply is provided topower CMM 10 thus providing a fully portable CMM. This is in contrast toprior art CMMs where power supply was based only on an AC cord. Inaddition, CMM 10 may also be powered directly by an AC cord through anAC/DC adapter via a conventional plug-in socket. As shown in FIGS. 2, 3and 25, a conventional rechargeable battery (e.g., Li-ion battery) isshown at 22. Battery 22 is mechanically and electrically connected intoa conventional battery support 252 which in turn is electricallyconnected to a conventional power supply and battery recharger circuitcomponent 254 located on circuit board 20. Also communicating with board20 is an on/off switch 258 (see FIG. 3) and a high-speed communicationport 259 (preferably a USB port). The joint electronics of arm 14 isconnected to board 20 using an RS-485 bus. Battery 22 can be charged ona separate charger, or charged in place in cradle 252 as is commonlyfound in conventional video cameras. It will be appreciated thatportable computer 172 (see FIG. 2) can operate a for several hours onits built-in batteries and/or in the alternative, may be electricallyconnected to the power supply unit 254 of CMM 10.

The on-board power supply/recharger unit in accordance with the presentinvention is preferably positioned as an integral part of CMM 10 bylocating this component as an integral part of base 12 and morespecifically as a part of the plastic base housing 26A, B. Note alsothat preferably, base housing 26A, B includes a small storage area 260having a pivotable lid 262 for storing spare batteries, probes, or thelike.

Turning now to FIGS. 4, 25 and 32-34, the novel magnetic mounting devicefor use with CMM 10 will now be described. This magnetic mounting deviceis shown generally at 24 in FIGS. 4, 25, 32 and 33. Magnetic mount 24includes a cylindrical non-magnetic housing 266 which terminates at itsupper end in a threaded section 268. As with all of the preferredthreading used in CMM 10, threading 268 is a tapered thread which isintended to be threadingly connected to threading 126 of first longjoint 16 as best shown in FIG. 25. Non-magnetic housing 266 has asubstantially cylindrical configuration with the exception of twolongitudinal extensions 270, 272 which are opposed from each other at180 o and extend outwardly and downwardly from housing 266. Attached oneither side of longitudinal extensions 270, 272 are a pair ofsemi-cylindrical housings 274, 276, each of which is formed from a“magnetic” material, that is, a material capable of being magnetizedsuch as iron or magnetic stainless steel. Together, “magnetic” housinghalves 274, 276 and longitudinal extensions 270, 272 form an open endedcylindrical enclosure for receiving and housing a magnetic core 278.Magnetic core 278 has an oblong shape with a non-magnetic center 280sandwiched between a pair of rare earth magnets (e.g.,neodymium-iron-boron) 282, 284. An axial opening 286 is provided throughnon-magnetic center 280. A circular cover plate 288 is positionedbeneath magnetic core 278 and located within the lower housing formed byelements 274, 276 and longitudinal extensions 270, 272. A shaft 290 ispositioned through a circular opening 291 in housing 266 and extendsdownwardly through axial opening 286 of magnetic core 278. Shaft 290 issupported for rotation by an upper bearing 292 and a lower bearing 294.Upper bearing 292 is received by an internal cylindrical recess inhousing 266 and lower bearing 294 is received by a similar cylindricalrecess in cover plate 288. A lever 296 extends outwardly andperpendicularly from shaft 290 and, as will be described hereafter,provides an on/off mechanism for the magnetic mount 264. Lever 296extends outwardly of housing 266 through a groove 297 through housing266 (see FIG. 25).

This entire assembly of lever 296, shaft 290 and bearings 292, 294 issecured together using an upper threaded fastener 298 and a lowerretaining ring 300. It will be appreciated that the various componentsof magnetic mount 264 are further secured by, for example, threadedfasteners 302 which connect housing 266 to “magnetic” material housingportions 274, 276 and threaded fasteners 304 which interconnect housingportions 274, 276 to cover 288. In addition, threaded fasteners 306attached longitudinal extensions 270, 272 of housing 266 to cover 288. Apin 308 is received by a lateral opening in core 278 and a lateralopening in shaft 290 so as to lock shaft 290 to core 278. In this way,as lever 296 is rotated, shaft 290 will rotate core 278 via shaftconnection 208.

As shown in FIGS. 1, 3 and 25, lever 296 is connected to a handle 310which is easily accessible on the exterior of base 12 and is used toactuate magnetic mount 264. To accomplish such actuation, handle 296 issimply moved (from the right to the left in FIG. 1). Movement of handle310 will in turn rotate lever 296 which in turn will rotate shaft 290which will then rotate rare earth magnets 282, 284 from theirnon-operative position (wherein magnets 282, 284 are aligned withnon-magnetic extensions 270, 272) into an actuated position wheremagnets 282, 284 are aligned with magnetic material 274, 276. When themagnets are aligned with the magnetic material as described, a magneticfield (flux) is formed. Similarly, when the magnets 282, 284 are out ofalignment with the magnetic material 274, 276, the flux path isinterrupted. In this state, the magnetic base can be separated from thetable upon which it sits. Note however that even in the non-alignedposition, there will be some residual magnetic flux. This small residualmagnetic flux in the “off” position is a positive feature of thisinvention as a small amount of magnetic flux acts to react with themagnet and automatically rotate lever 296 back to the “on” position whenreplaced on the table. It will be appreciated that when the magnets arein alignment with the magnetic material, a strong magnetic field will beestablished and semi-circular elements 274, 276 will be magneticallyadhered to the annular surface formed at the bottom thereof as shown at312 in FIGS. 25 and 33.

The magnetic mount 264 of the present invention provides a fullyintegrated yet removable mounting device since it is detachably mounted(via threading 268) and may be replaced by other attachments such as ascrew mount or vacuum mount. Of course, in order to be properly used,magnetic mount 264 must be placed on a magnetizable surface and beactivated (via lever 296) in order to operate. In the event thatmounting is required to a non-magnetic surface (e.g., granite), theninterface plates or other suitable mechanisms must be used between themagnetic base and the non-magnetic surface.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation.

1. A portable coordinate measurement machine (CMM) for measuring the position of an object in a selected volume, comprising: a manually positionable articulated arm having opposed first and second ends, said arm including a plurality of joints; a measurement probe attached to a first end of said articulated arm; an electronic circuit which receives the position signals from transducers in said arm and provides a digital coordinate corresponding to the position of the probe in a selected volume; and wherein at least one of said joints further comprise; a periodic pattern of a measurable characteristic; at least one read head spaced from and in communication with said pattern; said pattern and said read head being positioned within said joint so as to be rotatable with respect to each other; and at least one sensor which measures relative movement in said articulated arm with respect to said at least one read head so as to improve the measurement accuracy of said at least one read head.
 2. The CMM of claim 1 wherein: said at least one read head is in axial alignment with said at least one sensor.
 3. The CMM of claim 1 wherein said at least one sensor comprises a plurality of spaced sensors which measure displacement.
 4. The CMM of claim 1 wherein said at least one sensor comprises a sensor which measures displacement.
 5. The CMM of claim 4 including at least one sensor for measuring X-axis displacement of said pattern.
 6. The CMM of claim 5 including at least one sensor for measuring Y-axis displacement of said pattern.
 7. The CMM of claim 4 including at least one sensor for measuring Y-axis displacement of said pattern.
 8. The CMM of claim 4 wherein said at least one sensor comprises a proximity sensor.
 9. The CMM of claim 8 wherein said proximity sensor measures movement using at least one of Hall effects, magneto effects, resistive effects, capacitance and optics. 10.The CMM of claim 1 wherein said at least one joint includes a shaft surrounded, at least in part, by a housing, said shaft and said housing being adapted to rotate relative to one another, and wherein said at least one sensor includes at least one sensor for measuring relative movement between said shaft and said housing.
 11. The CMM of claim 10 including a plurality of sensors for measuring relative movement between said shaft and said housing.
 12. The CMM of claim 11 wherein said shaft is rotatable.
 13. The CMM of claim 12 wherein said at least one sensor includes: at least two sensors for measuring relative movement of said shaft including a first sensor for measuring X axis displacement and a second sensor for measuring Y axis displacement.
 14. The CMM of claim 13 wherein said plurality of sensors for measuring relative movement of said shaft further include a third sensor for measuring X axis rotation, a fourth sensor for measuring Y axis rotation and a fifth sensor for measuring Z axis displacement.
 15. The CMM of claim 14 wherein said at least one read head measures Z axis rotation of said shaft.
 16. The CMM of claim 14 wherein said third, fourth and fifth sensors are positioned at about 120 degrees with respect to each other.
 17. The CMM of claim 13 wherein said at least one read head measures Z axis rotation of said shaft.
 18. The CMM of claim 10 wherein said shaft is rotatable.
 19. The CMM of claim 10 including at least five sensors which, together with said read head, measure at least six degrees of freedom of said shaft.
 20. The CMM of claim 1 wherein said relative movement is caused by deformation to said arm.
 21. The CMM of claim 20 wherein said relative movement is caused by deformation of bearings in said joints.
 22. The CMM of claim 1 wherein said at least one sensor includes: at least two sensors which measure movement in said periodic pattern with respect to said at least one read head.
 23. The CMM of claim 22 wherein: said at least two sensors are positioned at about 90 degrees to each other.
 24. The CMM of claim 23 wherein: said at least two sensors comprise proximity sensors.
 25. The CMM of claim 1 wherein: said pattern comprises an optical fringe pattern; and said at least one read head comprises optical read head.
 26. The CMM of claim 25 wherein: said optical fringe pattern is disposed on an optical encoder disk.
 27. The CMM of claim 25 wherein said communication comprises: said read head detecting the interference between diffraction orders to produce sinusoidal signals from said read head inserted in said fringe pattern, said sinusoidal signals being electronically interpolated to detect displacement.
 28. The CMM of claim 1 wherein: said pattern of a measurable characteristic is at least one of the characteristics selected from the group consisting of reflectivity, opacity, magnetic field, capacitance, inductance and surface roughness.
 29. The CMM of claim 1 wherein said joints comprise long joints for swiveling motion and short joints for hinged motion.
 30. The CMM of claim 29 including three joint pairs, each joint pair comprising a long joint and a short joint.
 31. The CMM of claim 1 wherein said joints are arranged in the joint configurations selected from the group consisting of 2-2-2, 2-1-2, 2-2-3, and 2-1-3.
 32. The CMM of claim 1 wherein: said pattern is rotatable with respect to said at least one read head; and said at least one read head is stationary with respect to said pattern.
 33. The CMM of claim 1 wherein: said pattern is stationary with respect to said at least one read head; and said at least one read head is rotatable with respect to said pattern.
 34. The CMM of claim 1 wherein said joint further comprises: a first and second housing, and a rotatable shaft extending from said second housing into said first housing; a bearing disposed between said shaft and said first housing permitting said rotatable shaft to rotate within said first housing; said pattern being attached to said rotatable shaft; said at least one read head being fixed within said first housing such that rotation of the first housing with respect to the second housing causes said at least one read head to move relative to said pattern.
 35. The CMM of claim 34 wherein: said pattern is attached directly to said shaft.
 36. The CMM of claim 1 wherein said at least one joint comprises: a first housing; a second housing; a rotatable shaft fixed to said second housing and extending into said first housing; at least one bearing supported within said first housing and supporting said rotatable shaft for rotation about its axis; wherein one of said pattern and said at least one read head is fixed to an end of said shaft and the other of said pattern and said at least one read head is fixed within said first housing.
 37. The CMM of claim 1 wherein said arm includes at least five rotary joints such that said articulated arm has at least five degrees of freedom.
 38. The CMM of claim 37 wherein said at least one of said rotary joints comprises at least two of said rotary joints.
 39. The CMM of claim 37 wherein said at least one of said rotary joints comprises at least three of said rotary joints.
 40. The CMM of claim 37 wherein said at least one of said rotary joints comprises at least four of said rotary joints.
 41. The CMM of claim 37 wherein said at least one of said rotary joints comprises at least five of said rotary joints.
 42. The CMM of claim 37 including at least six rotary joints such that said articulated arm has at least six degrees of freedom and wherein said at least one of said rotary joints comprises at least six rotary joints.
 43. The CMM of claim 37 including at least seven rotary joints such that said articulated arm has at least seven degrees of freedom and wherein said at least one of said rotary joints comprises at least seven rotary joints.
 44. The CMM of claim 37 wherein said at least one of said rotary joints comprises all of said rotary joints.
 45. The CMM of claim 1 wherein said at least one of said rotary joints comprises at least two of said rotary joints.
 46. The CMM of claim 1 wherein said at least one of said rotary joints comprises at least three of said rotary joints.
 47. The CMM of claim 1 wherein said at least one of said rotary joints comprises at least four of said rotary joints.
 48. The CMM of claim 1 wherein said at least one of said rotary joints comprises at least five of said rotary joints.
 49. The CMM of claim 1 wherein said at least one of said rotary joints comprises at least six rotary joints.
 50. The CMM of claim 1 wherein said at least one of said rotary joints comprises at least seven rotary joints.
 51. The CMM of claim 1 wherein said at least one of said rotary joints comprises all of said rotary joints.
 52. A portable coordinate measurement machine (CMM) for measuring the position of an object in a selected volume, comprising: a manually positionable articulated arm having opposed first and second ends, said arm including a plurality of joints; a measurement probe attached to a first end of said articulated arm; an electronic circuit which receives the position signals from transducers in said arm and provides a digital coordinate corresponding to the position of the probe in a selected volume; and wherein at least one of said joints further comprise; a rotatable shaft surrounded, at least in part, by a housing, said shaft and said housing being adapted to rotate relative to one another; a periodic pattern of a measurable characteristic; at least one read head spaced from and in communication with said pattern; said pattern and said read head being positioned within said joint so as to be rotatable with respect to each other; and a plurality of displacement sensors which measure relative movement between said shaft and said housing, said relative movement measurement being used to improve the measurement accuracy of said at least one read head.
 53. The CMM of claim 52 including at least five sensors which, together with said read head, measure at least six degrees of freedom of said shaft.
 54. The CMM of claim 52 wherein said relative movement is caused by deformation to said arm.
 55. The CMM of claim 54 wherein said relative movement is caused by deformation of bearings in said joints.
 56. The CMM of claim 52 wherein said arm includes at least five rotary joints such that said articulated arm has at least five degrees of freedom.
 57. The CMM of claim 56 wherein said at least one of said rotary joints comprises at least two of said rotary joints.
 58. The CMM of claim 56 wherein said at least one of said rotary joints comprises at least three of said rotary joints.
 59. The CMM of claim 56 wherein said at least one of said rotary joints comprises at least four of said rotary joints.
 60. The CMM of claim 56 wherein said at least one of said rotary joints comprises at least five of said rotary joints.
 61. The CMM of claim 56 including at least six rotary joints such that said articulated arm has at least six degrees of freedom and wherein said at least one of said rotary joints comprises at least six rotary joints.
 62. The CMM of claim 56 including at least seven rotary joints such that said articulated arm has at least seven degrees of freedom and wherein said at least one of said rotary joints comprises at least seven rotary joints.
 63. The CMM of claim 56 wherein said at least one of said rotary joints comprises all of said rotary joints.
 64. The CMM of claim 52 wherein said at least one of said rotary joints comprises at least two of said rotary joints.
 65. The CMM of claim 52 wherein said at least one of said rotary joints comprises at least three of said rotary joints.
 66. The CMM of claim 52 wherein said at least one of said rotary joints comprises at least four of said rotary joints.
 67. The CMM of claim 52 wherein said at least one of said rotary joints comprises at least five of said rotary joints.
 68. The CMM of claim 52 wherein said at least one of said rotary joints comprises at least six rotary joints.
 69. The CMM of claim 52 wherein said at least one of said rotary joints comprises at least seven rotary joints.
 70. The CMM of claim 52 wherein said at least one of said rotary joints comprises all of said rotary joints. 